Ion vapor deposition apparatus and method

ABSTRACT

An ion vapor deposition (IVD) apparatus includes an IVD chamber, a vacuum pump for creating a vacuum in the chamber, and a source of ionizing gas. One or more target materials are mounted in the chamber and a holder is provided for holding the object to be coated. An electrical power source electrically biases the target materials. A mask covers the target materials and is movable relative to the target materials for selectively exposing respective target materials.

BACKGROUND OF THE INVENTION

This invention relates to ion vapour deposition (herein IVD) and relatesto a method of and apparatus for applying coatings by IVD.

The invention has particular reference to the application of coatings tooptical lenses of the type used in spectacle frames, and which mainlywill be corrective lenses, but could be plain lenses, but in fact theinvention it is believed will have a much wider application, at least inspecific aspects thereof, such that the invention can be applied to theapplication of coatings to other articles.

The lenses to which the invention applies may be of glass or plasticsmaterial.

As the main application as will be understood relates to the applicationof IVD coatings to spectacle lenses, reference will be made hereinafterexclusively or mainly to such a product and the coating thereof.

The IVD process comprises the placement of an article to be coated in achamber in which is provided a target of the coating material. Negativeelectric bias is applied to the target, and the chamber is filled withan inert gas, such as argon. Ionisation of the gas takes place, and thegas positive ions bombard the target by virtue of being attractedthereto due Ira the negative electric bias on the target. Sputtering ofthe target takes place which is a phenomenon resulting in the release ofparticles of the target material into the chamber atmosphere. Theseparticles then deposit on the surface of the article to be coated andmay be induced to deposit on the article by virtue of an electric biason the article or in the region of the chamber surrounding the article,and so a coating is built up.

IVD processes are of course well established for many products, and aretypically used for metallic products which require to be coated to ahigh degree of accuracy, and where the articles have to be used incontrolled environments or in situations where the performance of thearticles is critical. For example IVD coated articles such as screws,nuts and bolts may be used in the aircraft industry, in militaryapplications, or in space vehicle applications. The prior devices use atarget with one material attached to it. Therefore only one singlematerial can be sputtered from the target.

The use of IVD for the coating of spectacle lenses is also known.Coatings on spectacle lenses perform several functions. Firstly, areflection control coating serves to allow as much light of wavelengthin the visible range through the lens into the eye as possible, whilstreflecting as much light which is in the harmful wavelength region, suchas UV light, from the eye as possible. Other IVD coatings serve toprovide a hard protective surface to protect the lenses from scratchingand the like.

Generally speaking, the equipment which is used for IVD coating oflenses is large and is expensive, and requires considerable investmentin the part of a processor, and in commercial terms when a person ordersa pair of spectacles from an optician, he submits the prescription to alens manufacturer, but the lens manufacturer in turn will pass on thelenses to the IVD coating processor who will coat the lenses asrequired. Coating in the conventional machine can take as much as onehour.

SUMMARY OF THE INVENTION

The present invention arises out of the objective of providing arelatively small and inexpensive lens coating IVD machine, although itis recognised that some aspects of the invention have wider application.

In accordance with a first aspect of the invention, the apparatuscomprises a small IVD chamber for receiving lenses to be coated by IVD,said chamber having means for the introduction of ionising gas, a targetmaterial mounting in the chamber, and a lens mounting in the chamber,and further including a power source for electrically biassing thetarget mounting, which in turn serves to bias a target mounted thereon.

In one embodiment, the chamber is typically a rectilinear chamber ofdimensions in the range 30 cm diameter, and of appropriate height.

The chamber preferably has a viewing aperture by which the IVD processbeing performed therein can be observed.

The target mounting is preferably such as to be capable of selectivelypresenting a target of any one of two or more target materials to theionising gas so that, without removing the lenses or the targetmeterials from the chamber, layers of different target materials can bedeposited on the lenses in sequence. This selective utilisation ofdifferent target materials has wider application, and can be used in anyIVD processing system.

The mounting may comprise a mask or shield for covering the targetmaterials, said mask or shield being movable relative to differenttarget materials held by the mounting for selectively exposingrespective target materials.

Typical target materials which may be used in connection with thecoating of lenses comprise titanium dioxide and silicon dioxide forproviding the reflective coating on the lenses, and titanium forproviding the anti-scratch coating on the lenses. These coatings may belaid down on the lenses in sequence by appropriate operation of theapparatus.

The target mounting may comprise a first or main body in the form of ametallic block connected to the power source, said block preferablyhaving passages therein connected for the supply and return of coolingwater whereby the block may be water cooled. There may be a secondtarget mounting component serving to carry polarisation magnets of themounting, and a third target mounting part may comprise acompartmentalised disk having different compartments for receivingdifferent target materials, said disk co-operating with said mask forthe selective exposure of the different materials.

The power source may comprise a high voltage DC or radio frequency ACsupply for the charging of the target material.

Appropriate connections may be provided for the delivery and exhaust ofthe ionising gas.

The article mounting may comprise a cap which is conical orhemispherical and is made up of segments each adapted to carry aplurality of articles such as spectacle lenses, and the segments may berotatable so that both sides of the lenses carried thereby can betreated.

The article mounting may also be rotatable in order to ensure that thecoating material is applied evenly to the lens surfaces, and to enhancethe operation, a bias potential may be applied to the mounting In orderto attract the coating particles during IVD and improve adhesion.

The IVD can be further enhanced by providing inside the chamber afilament and cathode which are appropriately biased.

According to another aspect of the invention there is provided IVDapparatus comprising:

i) an IVD chamber for receiving articles to be coated by IVD;

ii) vacuum creating means for creating a vacuum in the chamber;

iii) gas introduction means for introducing ionising gas into thechamber;

iv) electric means for creating ion vapour discharge in the chamber;

v) a holder for holding articles to be IVD coated;

vi) at least two target material holding means in the chamber;

vii) high voltage biasing means for biasing the target holding means;

viii) target materials in said holding means;

ix) a shield means which is positionable between a first positioncovering one of the target materials whilst the other is sputtering, anda second position in which the other target material is covered whilstthe said one is sputtering;

x) means for moving the shield means between the first and secondpositions; and

xi) control means for detecting the build up of coating on the articleswhen the said one target is sputtering and for operating said means formoving when a predetermined build up of coating on said articles hastaken place, to terminate said sputtering of the said one target and topermit sputtering of said second target.

The holder for holding the articles to be coated may comprise a memberhaving apertures therein for holding individual ones of said articles,and preferabaly the member comprises a circular disc mounted forrotation in the chamber about its centre.

The target material holding means may comprise two magnetrons arrangedspaced and opposite in the chamber, each holding a target material, thesputtering surfaces of the materials, which surfaces are flat, being inthe same plane.

The shield may comprise a shield plate defining two arms whichrespectively cover the target materials in the first and secondpositions and in a preferred construction the shield plate may comprisea third arm, and the shield plate has a third position in which two ofthe arms of the plate cover the respective target materials.

The control means may comprise a crystal oscillator of which the crystalis located in the chamber adjacent the target materials to detect therate of sputtering thereby to determine the period during whichsputtering should take place to achieve the predetermined build-up ofcoating on the articles. The control means may be programmed orprogrammable to cause the shield to move between the first and secondpositions a number of times to cause the application of alternate,predetermined thickness layers of the target materials to the articles.

The various constructional features enable the machine of eachembodiment to provide coatings on lenses in a convenient and simplemanner, and such machines can be utilised on a "do-it-yourself" basis bylens manufacturers which means that lenses can be manufactured for usein a shorter time, and the lens manufacturers do not have theinconvenience of having to sub-contract the coating operation.

The various aspects of the invention are in the way of machine andapparatus features, and also in the various method steps involved inperforming the IVD operations. Aspects of the machine and method can beutilised as will be clearly understood in areas outside the area of lenscoating.

By way of example only, embodiments of the invention will now bedescribed with reference to the accompanying diagrammatic drawings,wherein:

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS

FIG. 1 is a sectional elevation of a machine according to one embodimentof the invention;

FIG. 2 is a sectional elevation of the target mounting of the machineshown in FIG. 1;

FIG. 3 is a side elevation of a machine according to another embodimentof the invention;

FIG. 4 is a perspective, partly cut away view of the IVD chamber of themachine of FIG. 3; and

FIGS. 5, 6 and 7 show in plan view the respective positions of theshield for the respective operational conditions of the machine shown inFIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring firstly to FIGS. 1 and 2 of the drawings, in FIG. 1 chamber 10may suitably be made of aluminium or steel plate, and the chamber isprovided with a lid 12 and a base 14. The chamber stands on a casing 15so that it will be located at a suitable working height. A typical sizedchamber will have the following dimensions; diameter=30 cm, height=35 cm

The chamber wall is provided with a viewing window 16 whereby the IVDprocess going on inside the chamber can be viewed. Such a viewing windowis not be necessary especially when the process is carried out underautomatic control, or if the chamber is constructed from glass, which isa possible embodiment of the invention.

The lid 12 supports an electric motor 18 which is drivingly connected toa mounting 20 inside the chamber by which the lenses to be coated may besupported. Rotation of motor 18 effects rotation at the appropriatespeed of the mounting 20. Such rotational speed may typically be 5-10r.p.m.

The mounting 20 is calotte shaped, and is made up of a number ofsegments 22 each of which is provided with a plurality of apertures 24for receiving the lenses to be coated. The lenses are held in theapertures so that one side of each lens so held faces downwardly intothe chamber. The individual segments 22 may be rotatable so as to bringthe other sides of the lenses into downwardly facing position. The lid12 may be electrically biased by the application of a suitable voltagethrough leads 26, which in turn biases the mounting 20 for the effectiveIVD coating on the lenses supported by the mounting 20, as will beexplained hereinafter.

The lid also is provided with an inlet valve 28 by which the ionisinggas may be introduced into the chamber 10. The flow of gas through valve28 is controlled by means of a pressure controller (not shown).

Also contained within the chamber 10 are an electron source in the formof a hot wire filament 30 and a positively biased probe 32. The use ofthis filament and probe raises the ionisation efficiency of the systemwhich leads to an improvement in the efficiency of ionisation by afactor of 100 in comparison with conventional diode arrangements.

The chamber 10 furthermore contains a target material holder 34 forsupporting the material which will be subjected to sputtering duringoperation in order to give off the particles which will eventually formthe coating on the lens surfaces. The target material holder 34 iselectrically biased through lead 37 by means of a high voltage DC orradio frequency AC generator 36 which is mounted in the casing.

The chamber 10 is evacuated using a turbo molecular pump 38 in serieswith a rotary pump 40, said pumps being contained within the casing 15.

In use, target materials are supported on target material holder 34, avacuum is pulled in the chamber by means of the pumps 38 and 40, thelenses to be coated are mounted on the segments 22, and ionising gas isintroduced into the chamber through valve 28. The utilisation of thefilament 30 and the probe 32 results in ionisation of the gas which isattracted to the high voltage biased material carried by target materialholder 34 which is then subjected to sputtering and the particles, suchas aluminium particles of the target are released into the atmosphere inthe chamber and are attracted to the mounting 20 and thereby coat thedownwardly facing surfaces of the lenses. At the appropriate time, thesegments 22 can be reversed for the coating of the opposite sides of thelenses. At the same time, the mounting 20 is rotated so that an evencoating is achieved.

The construction of target material holder 34 is shown in more detail inFIG. 2, and it is to be mentioned that the mounting is a magnetronsputtering target mounting. The mounting 34 consists of three mainparts. The first part 42 is a metallic block having passages 44 and 46through which cooling water may be circulated by virtue of the waterflowing inwardly through coupling 48 and exiting through discharge 50.The body 42 is subjected to the high voltage DC or radio frequencythrough lead 37, and it is well isolated from earth. The cooling watercirculates through the passages 44 and 46 in effecting the cooling ofthe body 42.

The body has a circumferential groove which is sealed by means of O-ringseal 52 and this seal is maintained in position by means of asurrounding metal ring 54. The main body 42 is connected to an earthdisc 56 through an insulator disc 58 and an earth casing 60 is connectedto the disk 56 and acts as a cathode shield. The earth disc is usedaround the sputtering target and at a small distance from it to preventarcing or discharge. If there is no such disc, arcing or discharge maytake place with the side walls of the sputtering target thus sputteringthe holder material and therefore contaminating the chamber.

The second part of the target mounting comprises a holder 62 whichhouses two magnets namely a solid disc magnet 64 which is arrangedcentrally of the holder 62, and an annular ring magnet 66 whichsurrounds disc 64 but is separated therefrom by an aluminium ring 68which lies between the two magnets and is machined in the body 62. Thebody 62 is screwed to the first body 42 to provide the necessary watercooling and electrical contacts. These magnets are used in thesputtering target to trap secondary electrons emitted from the targetsurface. This trapping increases the ionisation of the gas moleculesthus increasing the sputtering rate from the target surface.

The third part of the target material holder 34 is a body consisting ofa disc 70 which is divided into many compartments to house targetmaterials which may be the same or different. The disc 70 is screwed tothe second body 68. A mask 72 covers the disc 70 but is provided with atriangular cut-out which is positioned over the required section of thedisc 70 so that only the material which is facing the cut-out section isallowed to sputter at any one time. The mask is rotationally adjustablerelative to the disc so as to face the selected material for sputtering.The mask is located at a small distance from the disc 70 to prevent thegeneration of a flow discharge between the mask and the sputteringtarget. The sputtering target could be located in the top or lower baseof the chamber, or in any other convenient location in the chamber. Thetarget materials can be used in the form of solids or densely packedpowder bonded to a metal plate.

Argon is the gas mainly used for the chamber to create the discharge andsputtering. However, for reactive coating, argon reactive gas mixturesare used to provide the required reaction.

It will be appreciated that appropriate electrical insulation will beprovided in order to ensure the electrical effects. For example thedrive shaft which rotates the mounting 20 will be appropriatelyinsulated.

Referring now to FIGS. 3-7 which show another embodiment of theinvention, the machine shown in FIG. 3 comprises a casing 100 which asshown is divided vertically by a partition 102. The casing may typicallybe approximately 1.25 m sq in height and width, and it may typically be0.75 of a meter in depth. These dimensions give some idea of the size ofthe machine, as this machine is of a much smaller overall size comparedto the existing conventional machines for carrying out the same process.

The machine in the top right hand compartment is provided with the IVDchamber 104 which is of the configuration shown An FIG. 4 and describedhereinafter in greater detail. Also in the compartment As the turbomolelcular pump 106 which is connected in series via the duct 108 with arotary pump 110. To this pump is connected a trap 112 for the removal ofgases and moisture so that the atmosphere vacated from the chamber 104can be discharged into the surrounding air. To the underside of thechamber 104 is a gas inlet 114 and monitoring vacuum gauges 116 and 118also enter the base of the chamber.

Two motors 120 and 122 serve for rotating a target covering shieldcontained in the chamber and a holder plate for the lenses to be coated.A crystal detector 124 is contained in the chamber for detecting therate of sputtering and hence the rate of deposition of coating materialon the lenses for the automatic control of the process as will bedescribed.

A lid 126 closes the cheer, and the lid as shown clearly in FIG. 4 canbe swung to an open position to allow access to the interior of thechamber. The lid 126 has a viewing aperture 128 whereby the dischargeinside the chamber can be viewed but by virtue of the principle ofoperation of this machine such viewing aperture is not strictlynecessary as control of the process is automatic.

If reference is made now to FIG. 4, the chamber 104 wall be seen tocomprise a shallow cylindrical chamber which to one side has a deep wellportion 130 at the base of which Is an aperture 132 which couples to theturbo molelcular pump 106 whereby the chamber can be vacated.

On the base of the shallow portion of the chamber there are twoassemblies 134 and 136 which are magnetrons and also carry targetmaterials which are electrically biased for the sputtering effect to bedescribed herein. A drive shaft 138 passes through the base of thechamber and lies between the assemblies 134 and 136, and carries ashield plate 140. The shield plate 140 is T-shaped and has three arms142, 144 and 146 best seen in FIGS. 5-7. The shield plate 140 isdrivable about the axis of the shaft 138 by the motor 120 shown in FIG.1 and also FIG. 4 so that in fact the shield plate can be positioned inany of three positions shown respectively in FIGS. 5, 6 and 7. In factthe position shown in FIG. 5 is the third or park position in which thearms 144 and 146 respectively cover the target assemblies 134 and 136.In the position shown in FIG. 6, which is the first position, the shieldis turned clockwise from the FIG. 5 position through 90° so that thetarget 136 is exposed and the target 134 is covered by the arm 142. Inthe FIG. 7 or second position, the target 136 is covered whilst target134 is exposed. When a target is exposed it can sputter in order torelease particles for the coating of the lenses.

The lenses are carried by a circular disc 148 having apertures 150therein for receipt of the individual lenses and the disc 148 issupported on the axis of shaft 138, and is rotatable around said shaftaxis by means of the motor 122. The turning of the plate 148 during theprocess results in even coating of the lenses.

Reverting to FIG. 3, in the left hand side of the cabinet there areshelves supporting various control units comprising radio frequencypower unit 152 for powering the magnetrons 134, 136 with the targetmaterials. The radio frequency power unit operates at the order of 13.56MHz and at a power in the range 300-6000 watts. The unit 154 is a tunerfor the RF power unit and this tuner may be manually operated or may beunder automatic control.

A programmer 156 is provided whereby the machine can be programmed tocoat the lenses to a predetermined extent and in a predetermined manner,and the programmer is associated with a control alarm unit 158 and theunits 156 and 158 are coupled to the oscillator 124 for detection andautomatic control.

The unit 160 is a drive for the turbo molecular pump 106 and unit 162 isa pressure recording unit for recording the pressure in the cheer 104.

In the use of the apparatus, with the pumps off, the lid 126 is openedand the plate 148 is loaded with the lenses to be coated. The shield 140is in the third or park position shown in FIG. 5. The programmer 156 isprogrammed to give a preset sequence of coating operations and themachine is ready to be started. The lid 126 is closed and forms an airtight seal with the remainder of the chamber and then the pumps 106 and110 are switched on in order to pull the correct vacuum in the chamber104. In this example of the invention the required degree of vacuum 10⁻⁵torr is achieved approximately in 12 minutes. When the correct vacuumhas been achieved, the ionising gas is introduced into the chamber and aweak discharge is created in the chamber and around the lens to providea plasma which in fact bombards the lenses and cleans same. This plasmais generated by appropriate creation of electrical bias as described inrelation to the FIG. 1 embodiment by suitable filament and probe meanssuch as 30 and 32 provided inside the chamber. After a predeterminedperiod, the etching process is terminated. It might be mentioned thatprior to placement of the lenses an the chamber they may be cleanedusing a cleaning fluid such as IPA (iso propyl alcohol) and the etchingis a cold process carried out at room temperature. When one considersthis with the prior art method of precleaning favourable results areapparent, because in the prior art it is usual to initially etch thelenses using a caustic solution to which ultrasonic vibrations areapplied, followed by subsequent washings and treatment usingde-mineralised water, ultrasonic vibration being used at each stage.Subsequently a fluoron gas is used for vapour cleaning and thermalevaporation takes place at a temperature in the order of 1500°-1700° C.Furthermore in the prior method visual examination and checking musttake place at all times whereas with the method described above usingcold gas etching visual examination is not necessary. The cold gasetching is a sputtering process.

At the end of the initial cleaning step, the magnetrons are powered, andthe shield 140 is moved either to position 6 or position 7. The lensholder continues to be electrically biased whilst the magnetrons arepowered, and the exposed target starts to sputter and a first layer isdeposited on the lenses. When the thickness of the first layer reaches apredetermined value as determined by the programming and as detected bythe oscillator, the shield 140 is moved to the alternate positionexposing the other target and the process is repeated. As many layers ofthe respective targets and in any particular order can be deposited. Thecontroller for positioning the shield 140 is an optical controller 164carried by the shaft of the motor 120.

In the arrangement of FIG. 4, two sputtering target assemblies areshown, but At is possible to have more than two if required.

The power to the magnetrons may be cut off whilst the shield is beingrepositioned in order to prevent contamination of one target by theother.

At the end of the process, which is automatically controlled by theprogrammer 156 the power to the magnetrons is automatically switchedoff, and the chamber is vented to atmosphere. The venting may be suchthat the venting is controlled so that the machine may require a fewminutes before the lid 126 can be opened.

An advantage of the arrangement described is that the oscillator inmaintaining a monitor on the sputtering rate gives an excellent andreliable control on the thickness of each layer deposited. It is notnecessary to visually examine the sputtering as is often the case inconventional IVD apparatus.

As described in relation to the FIG. 1 embodiment, the magnetronassemblies are water cooled and an appropriate water circulation systemis provided for this purpose. The pumps in each embodiment preferablyalso are water cooled.

The utilisation of a third electrode in the chamber, as described inrelation to FIG. 1 improves the ionisation and sputtering effect inincreasing the ion collisions.

In a preferred feature of the embodiment described, the radio frequencyor high voltage DC signal for the magnetrons is supplied through thedrive shaft which may be insulated by a suitable bush from the chamberbase and there is effective sealing of the drive shaft from the base toenable high vacuums to be drawn inside the chamber.

As mentioned herein any feature of the FIG. 1 embodiment can be usedwhere appropriate In the FIG. 3 embodiment and vice versa, and theapplicant reserves the right to make a claim for any feature orcombination of features or method step or combination of method steps asdescribed herein whether such feature or method step or combination offeatures and method steps is or are derived from either or bothembodiments described.

The machines described have many advantages including but not limited tothe following.

1. Uniform and adherent multi-layered anti-reflection coatings can bedeposited on both sides of glass or plastic lenses.

2. Many thin layers can be deposited without interrupting the process.

3. By using thermionically assisted triode discharge it is possible tooperate at low gas base pressure thus making the processs more efficientand less expensive in terms of gas consumption.

4. It is possible to control indpenedently the lens holder bias, gaspressure, reactive gasses pressure and discharge current density.

5. Different reactive gasses could be employed to deposit various layersincluding "hard diamond" coating which is a carbon coating having ahardness similar to that of diamond.

6. Dense coating can be achieved by increasing the ionisation efficiencyand lowering the gas pressure.

7. Metals, semi-conductors and Insulators could be sputtered using theprocess.

8. The magnets of the sputtering target at least in the FIG. 1 and 2embodiment can be easily removed for maintenance or re-magnetisation.

9. Minimum temperature rise on the lenses during coating process. Accessfor thermal evaporation may be provided via extra holes in the baseplate of the vacuum chamber, by which extra electrodes can be insertedto provide the low tension necessary for thermal evaporation.

10. Thermal evaporation could be carried out in the same unit withminimum modification.

The equipment described is also suitable for pulsed gas mechanism toproduce reactive coatings. A pulsed gas mechanism occurs when gas ispulsed into the vacuum chamber rather than injected continuously. Thusthe discharge can be sustained using firstly low pressure inert gas thena reactive gas such as oxygen pulsed into the chamber in a flow thus forexample providing oxides. A reactive coating is a coating carried out inthe presence of a reactive gas to produce an oxide, nitride or carbide.A third electrode assembly can be used to support the discharge at lowargon pressure. The third electrode may be a metal plate inserted intothe chamber above the evaporation beats or sputtering target to enhancethe discharge. The plate Is positively biased to sustain the dischargeat low gas pressure.

I claim:
 1. An ion vapour deposition (IVD) apparatus comprising:i) anIVD chamber for receiving articles to be coated by IVD; ii) vacuumcreating means for creating a vacuum in the chamber; iii) gasintroduction means for introducing ionizing gas into the chamber; iv)electric means for creating ion vapour discharge in the chamber; v) aholder rotatably mounted in the IVD chamber for holding articles to beIVD coated; vi) at least first and second target material holding meansin the chamber; vii) a first target material and a second targetmaterial different from said first target material mounted in said firstand second target material holding means, respectively; viii) highvoltage biasing means for biasing the first and second target materialsin the first and second target material holding means so as to causesputtering of said first and second target materials; ix) control meansfor selectively controlling the sputtering of said first and secondtarget materials to provide a multi-layered coating on said articles tobe IVD coated; x) means for rotating the holder relative to the firstend second target material holding means during the sputtering of saidfirst and second target materials; xi) shield means covering said firstand second target materials and being movable to a plurality ofpositions to cause application of alternate selected thickness layers ofsaid first target material or said second target material.
 2. Anapparatus according to claim 1, wherein said chamber comprises acylindrical chamber.
 3. An apparatus according to claim 1, wherein theelectric means for creating ion vapour discharge includes a hot wirefilament and/or a positively biased probe.
 4. An apparatus according toclaim 3, wherein the holder for holding the articles to be coatedcomprises a disc having means for holding individual ones of saidarticles.
 5. Apparatus according to claim 1, wherein said first andsecond target material holding means comprises two spaced magnetronseach holding a target material, the sputtering surfaces of thematerials, which surfaces are flat, being in the same plane. 6.Apparatus according to claim 1 wherein said means for creating a vacuumcomprises a turbo molecular pump and a rotary pump in sequence adaptedto create a vacuum in the order of 10⁻⁵ torr.
 7. Apparatus according toclaim 1, wherein the control means comprises a crystal oscillator ofwhich the crystal is located in this chamber adjacent the targetmaterials to detect the rate of sputtering thereby to determine theperiod during which sputtering should take place to achieve thepredetermined build up of coating on the articles.
 8. Apparatusaccording to claim 1 wherein the chamber is of the order of 30-60 cm.